Area Forecast Discussion
Issued by NWS Paducah, KY

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408
FXUS63 KPAH 200216
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
916 PM CDT Tue Jun 19 2018

.UPDATE...
Issued at 915 PM CDT Tue Jun 19 2018

The KVWX Radar continues to show a slow progression of showers and
widely scattered thunderstorms across southern Illinois, generally
along the Interstate 64 corridor from Mount Vernon IL (KMVN)
northeast into west central Indiana. Both the KVWX and KPAH
(Paducah) WSR-88d radars indicate that the thunderstorms are
becoming more outflow dominated with the cold pool depth nearly
7kft above ground level.

Although bulk shear is quite weak (less than 15 knots through 5kft
agl) and lapse rates are marginal (less than 6C/KM), there
continues to be some weak forcing/mixing south of the outflows
from the thunderstorms. Isolated convective activity may still
persist at least through the midnight hour and shortly after
across the I-64 corridor into southwest Indiana and parts of
southwest Illinois.

Made some minor tweaks to clouds, winds, temperatures, dewpoints
and rain chances (PoPS) for the overnight hour in the digital,
tabular and text forecasts to reflect the minor trend change.

&&

.SHORT TERM...(Tonight through Wednesday)
Issued at 312 PM CDT Tue Jun 19 2018

Temperatures have struggled to reach 90 this afternoon and with
dewpoints holding around 70 heat indices are struggling to reach the
upper 90s, let alone triple digits. The lone exception is Mt Vernon,
Illinois where the dewpoint is in the middle 70s and the heat index
is 100.

Likewise we are still waiting for any convective development. Based
on the cu field at 20Z that will be most likely over southeast
Missouri, the Purchase Area and adjacent portions of southern
Illinois. However, the CAM data, in addition to the hills of
southeast Missouri, also show some convective activity glancing
along our northwest border regions from Perry County Missouri
through Jefferson County Illinois late this afternoon through
sunset. Have nothing but slight chances in these areas. Some more
isolated convective activity could linger around the I-64 corridor
through the night, but it should mostly stay north of our area.

The primary surface boundary will likely remain northeast of the
area through Wednesday, and the 12Z models seem to be trending a
little drier for Wednesday. Figure that the morning will remain dry,
with scattered convection developing, mainly in the north and
northeast, through the afternoon. Although there will be some
light westerly flow aloft, the shear will still be weak, so we
will continue with a largely disorganized heavy rainfall and
lightning threat.

Temperatures will be rather mild tonight with a lot of middle 70s
for lows mainly due to persistent southwest winds. Highs on
Wednesday will be a few degrees cooler than today due to increased
cloud cover and precipitation chances. Many locations will not
see 90 for the first time in quite awhile.

.LONG TERM...(Friday through Tuesday)
Issued at 312 PM CDT Tue Jun 19 2018

Wednesday night will be a transitional period across the region,
as we will be heading into a wet and cooler pattern through at
least the weekend. The 12Z GFS and ECMWF agree that one closed
upper storm system will move southeast though the Plains Wednesday
night and Thursday and then through our region on Friday. We will
see cooler temperatures aloft and should not have much trouble
getting good coverage of convection, especially during each daytime
period. We will have likely PoPs each day with good chances at
night.

We will get into weak southwest flow Wednesday night and that will
continue through Thursday night. If the upper low passes to the
north of the area Friday, as the 12Z ECMWF depicts, we could have
some decent westerly flow in the mid and upper-levels as a weak
surface trough moves through the area in the afternoon. A few
strong storms will be possible. If the low comes right overhead as
in the 12Z GFS, we will likely not see much severe potential.
Maybe some clear air funnels though.

We should dry out Friday night as the storm system exits to the
east of the area, but that will likely be short-lived. In the wake
of this system, we will be in a belt of modest mid/upper-level
flow with a series of disturbances moving into the area and
interacting with a leftover surface boundary. The ECMWF is a bit
faster with the onset of precipitation Saturday, while the GFS
indicates that we may stay dry over much of the region Saturday.
Either way it will be rather wet Saturday night and Sunday. With
the enhanced flow aloft, a few strong storms cannot be ruled out
if we can destabilize enough. That is in doubt given the expected
cloud cover and coverage of convection.

The GFS and ECMWF agree that a strong storm system will dive
southward through the northeast Sunday night and that will bring
an end to our precipitation and possibly bring a backdoor cold
front into the area. With both models developing rather amplified
ridging over our region, the backdoor cold front may have a hard
time scouring things out. Monday we will keep some small chance
PoPs in the southwest half of the area in case the boundary holds
up there. On Tuesday there is some potential for the boundary to
lift back across the area as a warm front, so we have some small
PoPs in the forecast then too. All in all we should be mostly dry
with somewhat more normal temperatures to start next week.

&&

.AVIATION...
Issued at 630 PM CDT Tue Jun 19 2018

Other than a few dissipating cumulus clouds, clear skies are
expected this evening. Southwest winds will diminish to less than 5
knots. Thunderstorms across central Missouri and Illinois may spread
some cirrus clouds across our region overnight, however no precip is
expected at the taf sites.

On Wednesday, there will be more in the way of cumulus development.
Mainly vfr conditions are expected. There is enough potential for
thunderstorms to mention them in the tafs during the afternoon. Any
storms could contain gusty winds and heavy rain.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

UPDATE...Smith
SHORT TERM...DRS
LONG TERM...DRS
AVIATION...MY



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